F322 - Energy Flashcards
What is the enthalpy change sign for an exothermic reaction?
Negative
What is meant by the term exothermic reaction?
A reaction in which heat energy is transferred to the surroundings.
What is meant by the term endothermic reaction?
A reaction in which heat energy is absorbed from the surroundings.
What is the enthalpy change sign for an endothermic reaction?
Positive
What is activation energy?
The energy barrier which must be overcome before a reaction can occur.
What is an example of an exothermic process?
Combustion or respiration
What is an example of an endothermic process?
Thermal decomposition
What are the standard conditions?
Pressure: 100kPa
Temperature: 298K
What is the enthalpy change of reaction?
The enthalpy change when amounts of reactants, as shown in the reaction equation, react together to give products in their standard states.
What is the enthalpy change of formation?
The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states.
What is the enthalpy change of combustion?
The enthalpy change when one mole of a fuel reacts completely with oxygen.
Which type of enthalpy process is bond breaking?
Endothermic
Which type of enthalpy process is bond making?
Exothermic
What is the average bond enthalpy?
The amount of energy needed to break one mole of a particular bond in one mole of gaseous molecules.
What is Hess’s law?
The total enthalpy change for a chemical reaction is independent of the route by which the reaction takes place, provides the initial and final conditions are the same.
What are the factors that affect the rate of a reaction?
- concentration
- temperature
- surface area
- catalysts
How does having a higher concentration increase the rate of a reaction?
More frequent collisions between reactant molecules.
How does having a higher temperature increase the rate of a reaction?
Molecules have more kinetic energy therefore more successful collisions between reactant molecules.
How does using a catalyst increase the rate of a reaction?
Activation energy is lowered therefore more molecules have the energy to overcome it leading to more successful collisions.
What is a catalyst?
Chemical which speeds up a her action without being consumed in the overall reaction.
Why are catalysts used?
Lower temperatures, reduce energy demands so therefore reduces carbon dioxide emissions from burning fossil fuels, allow for better atom economy processes to be used and can increase specificity (enzymes).
What does a Boltzmann distribution represent?
Number of molecules in a sample with a particular energy.
What are the key features of a Boltzmann distribution?
- no molecules have no energy
- majority of molecules have some energy
- few molecules have very low or very high energies
- area under the curve is the number of molecules with that particular energy
When does a dynamic equilibrium occur?
When the rate of the forward reaction is equal to the rate of the reverse reaction in a closed system.
What is Le Chatelier’s principle?
The equilibrium will shift so as to minimise the effect of a change applied to a closed system (e.g. concentration, pressure or temperature).
What does a catalyst do to a dynamic equilibrium?
Accelerates the rate at which the reaction achieves equilibrium as it will increase the rate of the forward and reverse reactions by the same amount.
How does changing the concentration affect the position of equilibrium?
Increase concentration: shifts away from where the increase occurs
Decrease concentration: shifts towards where the decrease occurs
How does changing the pressure affect the position of equilibrium?
Increase pressure: shifts to side with fewer moles (of gas)
Decrease pressure: shifts to side with more moles (of gas)
How does changing the temperature affect the position of equilibrium?
Increase temperature: shifts in direction of endothermic reaction
Decrease temperature: shifts in direction of exothermic reaction
